1. Field of the Invention
This invention relates to a rear stop type zoom lens, and more particularly to a retrofocus type zoom lens well compensated for aberration and constructed compactly in size.
2. Description of the Prior Art
In recent years, electronically controlled shutters have come to be adopted in an increasingly greater number of medium-priced cameras. Unlike the conventional mechanical shutters, shutters of this type are located wholly outside the lens systems and the sectors thereof can be concurrently used as stops. They are therefore advantageous in terms of structural simplicity and lower cost. Consequently, rear stop type lenses have come to find popular acceptance. If a rear stop type zoom lens capable of using such an electronically controlled shutter can be provided, this would make an immense contribution from the practical point of view because it would lead to successful incorporation of a zoom lens system in medium-priced cameras using electronically controlled shutters.
In this type zoom lens, however, the diaphragm is positioned externally to the rear and, moreover, the shutter is fixed in position on the camera body because of restrictions from the standpoint of mechanical structure. For this type zoom lens to secure a sufficient amount of marginal ray, therefore, it tends to be considerably greater size than a conventional zoom lens provided with an internal diaphragm. Besides, since the principal ray is separated greatly from the optical axis of the lens, compensation for astigmatism, comatic aberration, etc. is considerably more difficult than in an ordinary lens.